I just talked to another EA advisor about this issue. This is a fragment of our conversation:
( 12m 31s ) EA advisor: I highly admire your love for the game and had words with my team regarding your issue but sadly due to being old the in-game support for Battlefield 3 is sunset now and we are not left with any option to modify, unlock or grant and in game content manually.
( 13m 27s ) me: i understand
( 13m 52s ) me: i have 1 more question
( 14m 23s ) EA advisor: Sure! Please let me know.
( 15m 59s ) me: when was the last time EA advisors had the possibility to unlock content? some players managed to unlock it this way pretty recent, and told me to do the same...
( 18m 48s ) EA advisor: There was an update last year where the gun can not be unlocked or granted manually. I would suggest you to please check Answers HQ or any community website as many players reports the issues and their solution over there.
( 19m 43s ) me: ok, thank you for your time